A pendulum valve assembly generally includes a housing containing a pendulum valve and including an interior space and a pair of openings through which gaseous fluid can enter and exit the interior space. As its name implies, a pendulum valve pivots between open and closed positions, and includes a valve body, which is usually provided as a disk, connected to a rotatably shaft by a pivot arm. In a completely opened position the disk of the pendulum valve is moved out of the flow path defined by the openings so that fluid can enter and exit the interior space of the housing, while in a completely closed position the disk is moved into sealing contact with a valve seat surrounding one of the openings so that fluid can not enter the interior space.
The movement of the disk usually requires pivotal or rotational movement between a first angular position equal to the completely opened position and a second angular position, and then at least some translational movement from the second angular position into the completely closed position where the disk is in sealing contact with the valve seat. In order to obtain this combination of rotational and translational movement, prior pendulum valves have typically used multiple actuator elements which are inherently difficult to effect precise movement of the disk, and therefore more difficult to utilize for precise flow control purposes. For examples of such prior pendulum valves see the following: U.S. Pat. Nos. 2,850,260; 3,557,822; 3,722,857; 3,973,753; 4,052,036; 4,089,505; 4,333,631; 4,627,567; 4,785,844; 5,873,562; British Patent No. 1,050,435 and German Patent 1,190,755. Other valve structures are shown in U.S. Pat. Nos. 2,749,082; 3,854,696; 4,073,468; 4,088,301; 4,136,854; 4,395,049; 4,442,996; 4,458,905; 4,519,578; 4,921,213; 5,379,983; and 5,330,157.
U.S. patent application Ser. No. 09/339,084 discloses an improved pendulum valve assembly that is designed and constructed so as to eliminate the need for multiple actuator mechanisms. Instead, the improved pendulum valve assembly uses a simple rotating cam mechanism that precisely controls the rotational and axial movement of the valve body between a completely opened position and a completely closed position.
Pendulum valves are particularly useful in high purity gas delivery systems, such as those used in semiconductor manufacturing or other thin film coating processes performed at very low pressures (high vacuums), e.g., a pressure on the order of one torr or less. One ultra-high vacuum system adapted to operate at low conductances includes a vacuum pump separated from a process chamber by a pendulum valve, which helps control the pressure created in the process chamber by the vacuum pump within a predetermined range.
The process chamber of high purity gas delivery systems normally require cleaning after a given period of use. Such cleaning involves a physical scrubbing of the chamber surfaces and associated vacuum components, such as the pendulum valve that isolates the process chamber.
When the pendulum valve is cleaned it is necessary to shut down the vacuum pump and vent the entire system to atmosphere. Since the vacuum pump contains residues from the process conducted within the process chamber, venting to atmosphere exposes these residues to water vapor and other contaminants that may react with the residues to produce a corrosive agent that can lead to corrosion and premature failure of the vacuum pump. For example, using boron trichloride (BCl.sub.3) to etch an aluminum layer produces a residue of aluminum trichloride (AlCl.sub.3). When the aluminum trichloride residue reacts with water vapor in the atmosphere, an extremely corrosive hydrochloric acid (HCl) is produced.
As is known, such vacuum pumps are very expensive and difficult to replace. Accordingly there is a need for a device or means for isolating the vacuum pump from the atmosphere during cleaning of the process chamber and the pendulum valve.